Emscripten: resize canvas to 0x0 in DestroyWindow

Closest we can get to actually destroying it

src/video/emscripten/SDL_emscriptenvideo.c

@@ -293,6 +293,10 @@ Emscripten_DestroyWindow(_THIS, SDL_Window * window)
             data->egl_surface = EGL_NO_SURFACE;
         }
 #endif
+
+        /* We can't destroy the canvas, so resize it to zero instead */
+        emscripten_set_canvas_element_size(NULL, 0, 0);
+
         SDL_free(window->driverdata);
         window->driverdata = NULL;
     }